1 . Field of the Invention
The present invention relates generally to the prevention of deformities in circuit boards, such as printed circuit boards, and more specifically to preventing warpage in printed circuit boards in antennas.
2 . Description of the Related Art
In printed circuit boards (PCBs), integrated circuits, active components, passive components, and wiring are formed and/or placed onto one or both sides of an insulating base according to a predetermined pattern. Such PCBs are found in countless types of electronic equipment, running everything from portable radios to immense super-computers. Sophisticated boards may contain several layers of wiring to enable complex connectivity between the various components.
Boards are manufactured from a variety of board materials. The most commonly used material is a composition of glass fabrics or fibers bonded with epoxy resins. Other compositions used are made up of various other materials such as aramid fibers and polymide or polytetrafluoroethylene resins. However, these materials have been known to expand when subjected to heat from, for example wave soldering or exposure to the elements. In addition, such materials may be chipped or dropped and broken while being handled. Any such deformity may cause an electrical device to stop functioning properly. The problem of PCB warpage, or bending, is experienced in both the manufacture and use of PCBs. Since in most cases PCBs are secured in place (by pins or screws placed at the boards edges for example), any expansion will cause the board to bend or warp. Devices such as antennas, which are constantly exposed to the elements, are especially susceptible to this problem. Moreover, in the case of an antenna, any PCB warpage can potentially prevent the antenna from being able to receive transmissions properly, since the proper alignment and shape of the PCB is often essential to the antenna""s proper function.
Typically, the problem of PCB warpage or bending is dealt with by providing xe2x80x9cboard stiffenersxe2x80x9d, which are rigid in a direction generally perpendicular to the plane of the board. The fundamental nature of these separate board stiffeners is to act as common mechanical support members secured to the board, much like beams in the shape of an xe2x80x9cIxe2x80x9d(I-beams) or xe2x80x9cLxe2x80x9d(L-beams) in larger mechanical structures. Board stiffeners are installed at selected locations, generally both longitudinally and crosswise, to ensure that the board remains planar. A typical board stiffener comprises an elongated metallic bar which is mounted in a fixed relationship onto the upper or bottom surface of the board. To securely affix the stiffener to the board in an appropriate position, typical installation makes use of a conventional fastening technique, such as riveting or soldering, at a plurality of locations on the board. In most cases, the stiffener is constructed of an electrically conductive material. This allows the board stiffener to function as a power distributor or as a common electrical ground for a portion of the circuitry embodied within the board, in addition to providing a mechanical function. There are many different board stiffener structures, such as grooved wrap-around frames. A grooved wrap-around frame is a frame that supports the entire perimeter of a PCB with engaging tabs that fit through the PCB, and are bent over on the opposite side of the board.
However, in many cases, the board stiffeners themselves or indeed the entire casing of an electronic device, may be subject to the same aforementioned distortions and deformations. These may result in stress-induced warpage of a PCB.
Another solution is to provide PCBs that have low expansion factors, leading to reduced likelihood of PCB warpage. These warp-resistant PCBs, however, tend to be more expensive than typical PCBs.
It would be advantageous to have a method and apparatus that would significantly reduce PCB warpage. It would also be advantageous to provide solutions to maintain proper PCB alignment and shape in an antenna despite the PCBs possible expansion due to the influence of the elements. Furthermore, it would be advantageous to provide such solutions with relatively inexpensive PCBs for use in devices, such as antennas, that are exposed to the elements.
The present invention provides a method and apparatus for holding in place a printed circuit board (PCB) so as to prevent the PCB from warping. The method entails fastening a PCB to a base structure, placing a frame over the PCB, and securing the frame to the base at a single point in the relative center of the PCB. The apparatus comprises a base to which a PCB is fastened and a frame overlaying the PCB and secured to the base.
The advantage of this invention is that a PCB may expand in the XY plane without the expansion causing the PCB to warp. Only expansion in the Z direction is substantially restricted. Also, since the PCB is allowed to expand, the PCB may be constructed of materials that are cheaper than those materials that are more resistant to warpage. Moreover, a board stiffener need not be attached to the PCB.